There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

The method we introduced in 1992 for measuring hardness and elastic modulus by instrumented indentation techniques has widely been adopted and used in the characterization of small-scale mechanical behavior. Since its original development, the method has undergone numerous refinements and changes brought about by improvements to testing equipment and techniques as well as from advances in our understanding of the mechanics of elastic–plastic contact. Here, we review our current understanding of the mechanics governing elastic–plastic indentation as they pertain to load and depth-sensing indentation testing of monolithic materials and provide an update of how we now implement the method to make the most accurate mechanical property measurements. The limitations of the method are also discussed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400085800

Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology

Bulk nanostructured materials from severe plastic deformation

https://dc.engconfintl.org/cgi/viewcontent.cgi?article=1032&context=superalloys_ii

A critical review of high entropy alloys and related concepts

The present work investigates the feasibility of microwave sintering to produce bulk metal-based nanocomposites having blend composition of Cu 99 Cr 1 , Cu 94 Cr 6 , Cu 99 Cr 1 –4 wt.% SiC and Cu 94 Cr 6 –4 wt.% SiC (average particle size ∼30 nm). The 50 h ball-milled samples were uniaxially pressed, and then pellets were sintered at 800 °C, 900 °C and 1000 °C for a constant soaking period of 30 min by microwave sintering technique. Microstructural characterization was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Sintered compacts resulted a highly densified compacts (∼95% relative density) while retaining ultra-fine grains (100–200 nm) in the matrix. The mechanical properties, namely, hardness and wear resistance, and electrical conductivity of the sintered specimens were also evaluated. The best combination of mechanical properties (e.g. hardness ∼2.4 GPa) and electrical conductivity (60.3% of IACS) were obtained for Cu 94 Cr 6 –4 wt.% SiC sintered at 900 °C. This is possibly due to presence of ultra-fine grains in the bulk samples, good densification and proper bonding between particles. The results were analyzed in the light of interactions of microwaves between metallic matrix and microwave susceptive SiC particulates.

Mechanical properties and electrical conductivity of Cu–Cr and Cu–Cr–4% SiC nanocomposites for thermo-electric applications

Attempts have been made to synthesize Cu 99 Cr 1 , Cu 94 Cr 6 , Cu 99 Cr 1 –4% SiC and Cu 94 Cr 6 –4% SiC (∼30 nm) nanocomposites for thermo-electric applications. The blend compositions were ball-milled for 50 h in a stainless steel grinding media. The microstructural features were characterized by X-ray diffraction (XRD), Nano zeta sizer, Fourier transforms infrared radiation, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Analysis of crystallite size, lattice microstrain and lattice parameter of Cu revealed that the dissolution of Cr increased up to 1 at.% in presence of nanosize SiC particles during milling. The compact specimens were subjected to vacuum sintering (900 °C and 1000 °C for 1 h), and the results were compared with that of microwave sintered samples. The mechanical properties like Vickers hardness and electrical conductivity of the sintered specimens were also investigated.

Structural investigation of vacuum sintered Cu–Cr and Cu–Cr–4% SiC nanocomposites prepared by mechanical alloying

A nanostructured SiC coating was prepared on the surface of carbon fibers by slurry coating and in situ reaction sintering. Phases of the coating were identified by X-ray diffraction, and features and structure were investigated by scanning electron microscopy and transmission electron microscopy. The oxidation resistant properties of the carbon fibers with and without the SiC coating were studied using isothermal oxidation. The results show that the nanostructured SiC coating was uniform and its coverage was complete. The oxidation activation energy of the fibers increased about 25% and the oxidation resistant of the coated fibers increases significantly.

Oxidation protection of carbon fibers by a reaction sintered nanostructured SiC coating

Mechanical Milling and Alloying

Nanocrystalline (nc) Al-Pb two phase mixtures of different Pb concentrations were made by two different routes using high energy ball milling. The microhardness measurements show a softening in nc Al-Pb composites with the increase in Pb content, contradicting the previous results reported in the literature. We conclude that interaction of Pb atoms with nanocrystalline Al grain boundaries is responsible for the softening of the nc Al matrix observed in the current study.

Carl C. Koch

Papers

Mechanical properties and electrical conductivity of Cu–Cr and Cu–Cr–4% SiC nanocomposites for thermo-electric applications

Structural investigation of vacuum sintered Cu–Cr and Cu–Cr–4% SiC nanocomposites prepared by mechanical alloying

Oxidation protection of carbon fibers by a reaction sintered nanostructured SiC coating

Mechanical Milling and Alloying

Effect of Pb on the Mechanical Properties of Nanocrystalline A1